Co-extruded, multi-layered battery separator

ABSTRACT

A battery separator comprises a co-extruded, microporous membrane having at least two layers made of extrudable polymers and having: a uniform thickness defined by a standard deviation of &lt;0.80 microns (μm); or an interply adhesion as defined by a peel strength &gt;60 grams.

RELATED APPLICATION

This application is a divisional application claiming the benefit ofco-pending U.S. patent application Ser. No. 15/979,679, filed May 15,2018, which claims priority to U.S. application Ser. No. 11/560,911filed Nov. 17, 2006, now U.S. Pat. No. 10,003,058, Issued Jun. 19, 2018,the references which are incorporated herein.

FIELD OF THE INVENTION

The battery separator disclosed herein is a co-extruded, multi-layeredbattery separator. One embodiment of this separator may be used inlithium ion batteries.

BACKGROUND OF THE INVENTION

Multi-layered battery separators are disclosed in, for example, U.S.Pat. Nos.: 4,650,730; 5,240,655; 5,281,491; 5,691,047; 5,691,077;5,952,120; 6,080,507; 6,878,226; and U.S. Patent Publication No.20020136945.

While several of the foregoing references mention that multi-layeredseparators may be made by a co-extrusion process, in commercialpractice, the co-extrusion process has been difficult to implement on acommercial basis. Particularly, the products of previous co-extrusiontrials have been fraught with uniformity issues that have inhibited thecommercialization of products made by that process. These issues, it isbelieved, arise from the intricacies associated with simultaneouslyextruding at least two dissimilar polymers through a narrow orifice die.Accordingly, the prior attempts to produce a co-extruded, multi-layeredbattery separator have yielded non-uniform product. As such, noco-extruded, multi-layered battery separators are commerciallyavailable.

Therefore, there is a need for a co-extruded, multi-layered batteryseparator having uniform physical properties.

SUMMARY OF THE INVENTION

A battery separator comprises a co-extruded, microporous membrane havingat least two layers made of extrudable polymers and having: a uniformthickness defined by a standard deviation of <0.80 microns (μm); or aninterply adhesion as defined by a peel strength >60 grams.

DESCRIPTION OF THE INVENTION

The instant battery separator shall be described with regard to use insecondary lithium ion batteries (e.g., those used in cell phones, laptopcomputers, and other devices requiring a light-weight charge storagedevice). It being understood, however, that the invention is not solimited and the instant battery separator may be used in other batterysystems (e.g., NiMH, NiCd, alkaline, primary lithium, to name a few).

In general, battery separators for use in lithium ion batteries aremicroporous membranes having the following typical physical properties:thickness—less than 5 mils (125 μm), or less than 2 mils (50 μm), orless than 1 mil (25 μm), the practical lower limit is about ⅓ mil (8μm); puncture strength—greater than 400 grams, or greater than 550grams; average pore sizes—0.005-10.000 μm, or 0.01-5.00 μm, or 0.05-2.00μm; Gurley values (ASTM-D726(B))—5-100 seconds, or 10-60 seconds.

The instant battery separator is a co-extruded, multi-layered batteryseparator. Co-extruded refers to a process where polymers aresimultaneously brought together in an extrusion die and exit from thedie in a form, here a generally planar structure, having at least twodiscrete layers joined together at the interface of the discrete layersby, for example, a commingling of the polymers forming the interface ofthe discrete layers. The extrusion die may be either a flat sheet (orslot) die or a blown film (or annular) die. The co-extrusion processshall be described in greater detail below. Multi-layered refers to aseparator having at least two layers. Multi-layered may also refer tostructures with 3, 4, 5, 6, 7, or more layers. Each layer is formed by aseparate polymer feed stream into the extrusion die. The layers may beof differing thicknesses. Most often, at least two of the feed streamsare of dissimilar polymers. Dissimilar polymer refers to: polymershaving dissimilar chemical natures (e.g., PE and PP, or PE and aco-polymer of PE are polymers having dissimilar chemical natures);and/or polymer having the same chemical nature but dissimilar properties(e.g., two PE's having differing properties (e.g., density, molecularweights, molecular weight distributions, rheology, additives(composition and/or percentage), etc.)) However, the polymers may be thesame or identical.

The polymers that may be used in the instant battery separator are thosethat are extrudable. Such polymers are typically referred to asthermoplastic polymers. Exemplary thermoplastic polymers include, butare not limited to: polyolefins, polyacetals (or polyoxymethylenes),polyamides, polyesters, polysulfides, polyvinyl alcohols, polyvinylesters, and polyvinylidenes. Polyolefins include, but are not limitedto: polyethylene (including, for example, LDPE, LLDPE, HDPE, UHDPE),polybutylene, polymethylpentane, co-polymers thereof, and blendsthereof. Polyamides (nylons) include, but are not limited to: polyamide6, polyamide 66, Nylon 10,10,polyphthalamide (PPA), co-polymers thereof,and blends thereof. Polyesters include, but are not limited to:polyester terephalthalate, polybutyl terephalthalate, co-polymersthereof, and blends thereof. Polysulfides include, but are not limitedto, polyphenyl sulfide, co-polymers thereof, and blends thereof.Polyvinyl alcohols include, but are not limited to: ethylene-vinylalcohol, co-polymers thereof, and blends thereof. Polyvinyl estersinclude, but are not limited to, polyvinyl acetate, ethylene vinylacetate, co-polymers thereof, and blends thereof. Polyvinylidenesinclude, but are not limited to: fluorinated polyvinylidenes (e.g.,polyvinylidene chloride, polyvinylidene), co-polymers thereof, andblends thereof.

Various materials may be added to the polymers. These materials areadded to modify or enhance the performance or properties of anindividual layer or the overall separator. Such materials include, butare not limited to:

Materials to lower the melting temperature of the polymer may be added.Typically, the multi-layered separator includes a layer designed toclose its pores at a predetermined temperature to block the flow of ionsbetween the electrodes of the battery. This function is commonlyreferred to as ‘shutdown.’ In one embodiment, a trilayer separator has amiddle shutdown layer. To lower the shutdown temperature of the layer,materials, with a melting temperature less than the polymer to whichthey are mixed, may be added to the polymer. Such materials include, butare not limited to: materials with a melting temperature less than 125°C., for example, polyolefins or polyolefin oligomers. Such materialsinclude, but are not limited to: polyolefin waxes (polyethylene wax,polypropylene wax, polybutene wax, and blends thereof). These materialsmay be loaded into the polymer at a rate of 5-50wt % of the polymer.Shutdown s obtainable in one embodiment. Shutdown temperatures below130° C. are obtainable in other embodiments.

Materials to improve the melt integrity of the membrane may be added.Melt integrity refers to the ability of the membrane to limit its lossor deterioration of its physical dimension at elevated temperatures suchthat the electrodes remain physically separated. Such materials includemineral fillers. Mineral fillers include, but are not limited to: talc,kaolin, synthetic silica, diatomaceous earth, mica, nanoclay, boronnitride, silicon dioxide, titanium dioxide, barium sulfate, calciumcarbonate, aluminum hydroxide, magnesium hydroxide and the like, andblends thereof. Such materials may also include, but are not limited to,fine fibers. Fine fibers include glass fibers and chopped polymerfibers. Loading rates range from 1-60 wt % of the polymer of the layer.Such materials may also include high melting point or high viscosityorganic materials, e.g., PTFE and UHMWPE. Such materials may alsoinclude cross-linking or coupling agents.

Materials to improve the strength or toughness of the membrane may beadded. Such materials include elastomers. Elastomers include, but arenot limited to: ethylene-propylene (EPR), ethylene-propylene-diene(EPDM), styrene-butadiene (SBR), styrene isoprene (SIR), ethylidenenorbornene (ENB), epoxy, and polyurethane and blends thereof. Suchmaterials may also include, but are not limited to, fine fibers. Finefibers include glass fibers and chopped polymer fibers. Loading ratesrange from 2-30 wt % of the polymer of the layer. Such materials mayalso include cross-linking or coupling agents or high viscosity or highmelting point materials.

Materials to improve the antistatic properties of the membrane may beadded. Such materials include, for example, antistatic agents.Antistatic agents include, but are not limited to, glycerolmonostreates, ethoxylated amines, polyethers (e.g., Pelestat 300,commercially available from Sanyo Chemical Industrial of Japan). Loadingrates range from 0.001-10 wt % of the polymer of the layer.

Materials to improve the surface wettability of the separator may beadded. Such materials include, for example, wetting agents. Wettingagents include, but are not limited to, ethoxylated alcohols, primarypolymeric carboxylic acids, glycols (e.g., polypropylene glycol andpolyethylene glycols), polyolefin functionalized with maleic anhydride,acrylic acid, glycidyl methacrylate. Loading rates range from 0.01-10wt% of the polymer of the layer.

Materials to improve the surface tribology performance of the separatormay be added. Such materials include lubricants. Lubricants include, forexample, fluoropolymers (e.g., polyvinylidene fluoride,polytetrafluoroethylene, low molecular weight fluoropolymers), slipagents (e.g., oleamide, stearamide, erucamide, Kemamide®, calciumstearate, silicone. Loading rates range from 0.001-10wt % of the polymerof the layer.

Materials to improve the polymer processing may be added. Such materialsinclude, for example, fluoropolymers, boron nitride, polyolefin waxes.Loading rates range from 100 ppm to 10 wt % of the polymer of the layer.

Materials to improve the flame retardant nature of the membrane may beadded. Such materials include, for example, brominated flame retardants,ammonium phosphate, ammonium hydroxide, alumina trihydrate, andphosphate ester.

Materials to facilitate nucleation of the polymer may be added. Suchmaterials include nucleating agents. Nucleating agents include, but arenot limited to, sodium benzoate, dibenzylidene sorbitol (DBS) and itchemical derivatives. Loading rates are conventional.

Materials to color the layers may be added. Such materials areconventional.

In the manufacture of the instant battery separator, the polymers areco-extruded to form a multi-layered, nonporous precursor, and then theprecursor is processed to form the micropores. Micropores may be formedby a ‘wet’ process or a ‘dry’ process. The wet process (also referredas: solvent extraction, phase inversion, thermally induced phaseseparation (TIPS), or gel extraction) generally involves: the additionof a removable material prior to the formation of the precursor, andsubsequently removing that material, for example, by an extractionprocess to form the pores. The dry process (also referred to as theCelgard process) generally involves: extruding a precursor (notincluding any removal material for pore formation); annealing theprecursor; and stretching the precursor to form the micropores. Theinstant invention will be discussed hereinafter with regard to the dryprocess.

To obtain the uniform dimensional properties of the instant co-extruded,multi-layered battery separator, an extrusion die having a specificshear rate was used. It was determined that the shear rate of the diemust be at a minimum 4/sec at a throughput of 18-100 lbs/hr (8.2-45.4Kg/hr) per layer. In one embodiment, the shear rate was ≥8/sec at athroughput of 18-100 lbs/hr (8.2-45.4 Kg/hr) per layer. All otherparameters are those conventionally known.

EXAMPLES

The foregoing invention is further illustrated in the followingexamples. Table 1 illustrates 11 samples made according to the foregoingdiscussion of the invention. Table 2 illustrates the use of variousmaterials to improve the melt integrity of the separator to a separatorwithout such material. Table 3 illustrates the use of other of theforegoing materials to improve various properties of the separator. Thetest procedures used in compiling the information in the Tables is setout below.

Test Procedures

Gurley: Gurley was measured by two methods. In the first method definedas the Japanese Industrial Standard Gurley (JIS Gurley), Gurley ismeasured using the OHKEN permeability tester. JIS Gurley is defined asthe time in seconds required for 100 cc of air to pass through onesquare inch of film at constant pressure of 4.8 inches of H₂O. In thesecond method, Gurley is measured according to the ASTM D-726 procedureand is defined as the time in seconds required for 10 cc of air to passthrough one square inch of film at constant pressure of 4.8 inches ofH₂O.

Tensile properties: MD and TD Tensile strength is measured using InstronModel 4201 according to ASTM-882 procedure.

Puncture strength: Puncture strength is measured using Instron Model4442 based on ASTM D3763. The units of puncture strength are newtons.The measurements are made across the width of stretched product and theaveraged puncture energy (puncture strength) is defined as the forcerequired to puncture the test sample.

Peel Strength or Adhesion: Intra-layer adhesion is tested using theChatillon TCD-200 Peel Force Tester.

Shrinkage: Shrinkage is measured at 90° C. for 60 minutes using amodified ASTM D-2732-96 procedure.

Thickness: The membrane thickness values are measured using the EmvecoMicrogage 210-A precision micrometer according to ASTM D374. Thicknessvalues are reported in units of micrometers (μm). 20 individualmicrometer readings taken across the width of the sample are averaged.

Porosity: The porosity of the microporous film is measured by methodASTM D2873.

High Temperature Melt Integrity: High Temperature Melt Integrity ismeasured using Thermal Mechanical Analysis (TMA). The TMA compressionprobe is used to measure the thickness change of a separator undercompression at a constant load of 125 gm as the temperature is scannedfrom 25 to 300° C. at a rate of 5° C./min. The percentage of thicknessretained at 250° C. is defined as the high temperature meltingintegrity.

Wettability: One drop of a typical lithium ion electrolyte is placed ona sample of the membrane. The change in appearance of sample from opaqueto nearly transparent is recorded. For the wettable separator,appearance should be nearly uniform translucent with no opaque areas. Anon-wettable sample retains its opacity.

ER (Electrical Resistance): The units of electrical resistance areohm-cm². The separator resistance is characterized by cutting smallpieces of separators from the finished material and then placing thembetween two blocking electrodes. The separators are completely saturatedwith the battery electrolyte with 1.0M LiPF₆ salt in EC/EMC solvent of3:7 ratio by volume. The resistance, R (Ω) of the separator is measuredby 4-probe AC impedance technique. In order to reduce the measurementerror on the electrode/separator interface, multiple measurements areneeded by adding more separator layers. Based on the multiple layermeasurements, the electrical (ionic) resistance, R_(s) (Ω) of theseparator saturated with electrolyte is then calculated by the formula,

$\begin{matrix}{R_{s} = \frac{\rho_{s}l}{A}} & (1)\end{matrix}$

where ρ_(s) is the ionic resistivity of the separator in Ω-cm, A is theelectrode area in cm² and / is the thickness of the separator membranein cm. The ratio ρ_(s)/A is the slope calculated for the variation ofseparator resistance (ΔR) with multiple separator layers (Δδ) which isgiven by,

$\begin{matrix}{{slope} = {\frac{\rho_{s}}{A} = {\frac{\Delta R}{\Delta \delta}.}}} & (2)\end{matrix}$

Also see U.S. patent application Ser. No. 11/400,465 filed Apr. 7, 2006,test procedure related to ‘ionic resistance’, incorporated herein byreference.

Pin Removal: The pin removal test simulates the cell winding process.Pin Removal force is the force in grams required to pull the pin fromthe center of jelly roll after winding. A battery winding machine wasused to wind the separator around a pin (or core or mandrel). The pin isa two (2) piece cylindrical mandrel with a 0.16 inch diameter and asmooth exterior surface. Each piece has a semicircular cross section.The separator, discussed below, is taken up on the pin. The initialforce (tangential) on the separator is 0.5 kgf and thereafter theseparator is wound at a rate of ten (10) inches in twenty four (24)seconds. During winding, a tension roller engages the separator beingwound on the mandrel. The tension roller comprises a ⅝″ diameter rollerlocated on the side opposite the separator feed, a ¾″ pneumatic cylinderto which 1 bar of air pressure is applied (when engaged), and a ¼″ rodinterconnecting the roller and the cylinder. The separator consists oftwo (2) 30 mm (width)×10″ pieces of the membrane being tested. Five (5)of these separators are tested, the results averaged, and the averagedvalue is reported. Each piece is spliced onto a separator feed roll onthe winding machine with a 1″ overlap. From the free end of theseparator, i.e., distal the spliced end, ink marks are made at ½″ and7″. The ½″ mark is aligned with the far side of the pin (i.e., the sideadjacent the tension roller), the separator is engaged between thepieces of the pin, and winding is begun with the tension roller engaged.When the 7″ mark is about ½″ from the jellyroll (separator wound on thepin), the separator is cut at that mark, and the free end of theseparator is secured to the jellyroll with a piece of adhesive tape (1″wide, ½″ overlap). The jellyroll (i.e., pin with separator woundthereon) is removed from the winding machine. An acceptable jellyrollhas no wrinkles and no telescoping. The jellyroll is placed in a tensilestrength tester (i.e., Chatillon Model TCD 500-MS from Chatillon Inc.,Greensboro, N.C.) with a load cell (50 lbs×0.02b; Chatillon DFGS 50).The strain rate is 2.5 inches per minute and data from the load cell isrecorded at a rate of 100 points per second. The peak force is reportedas the pin removal force. Also see: U.S. Pat. No. 6,692,867,incorporated herein by reference.

Dielectric Breakdown: Voltage is increased on a sample until adielectric breakdown of the material is observed. Dielectric Breakdownis expressed in volts. A separator is placed between two electrodes anda voltage is applied across the electrodes. The voltage is increaseduntil dielectric breakdown of the separator is observed. Strongseparators show high failure voltage. Any non-uniformity can lead to alow failure voltage.

Aquapore Size: Pore size is measured using the Aquapore availablethrough PMI (Porous Materials Inc.). Pore size is expressed in microns,μm.

Mixed Penetration: Mixed penetration is the force required to create ashort through a separator and is expressed in kilogram-force, kgf. Mixedpenetration is the force required to create a short through a separatordue to mixed penetration. In this test one starts with a base of a firstmetal plate, on top of this plate is placed a sheet of cathode material,on top of cathode is placed a separator, and on top of the separator isplaced a sheet of anode material. A ball tip of 3 mm is then providedattached to a force gauge. The ball tip is connected to the first metalplate by a resistance meter. Pressure is applied to the ball tip, whichis recorded on the force gauge. Once force is applied, there builds upan anode mix and a cathode mix on either side of the separator. When theresistance falls dramatically it indicates a short through the separatordue to mixed penetration. Mixed penetration measures the strength of theseparator and resistance towards mixed penetration. This has been foundto more accurately simulate the behavior of a real cell. It is a betterindicator than puncture strength of how a separator will behave in acell. This test is used to indicate the tendency of separators to allowshort-circuits during battery assembly. Also see U.S. patent applicationSer. No. 11/400,465 filed Apr. 7, 2006, incorporated herein byreference.

TABLE 1 Examples of Bilayer & Trilayer Microporous Membrane SampleCelgard Sample Sample Sample Sample Sample Sample Sample Sample SampleSample Sample Number 2300 ® #1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 PP/PE/PPP/PE/ PP/PE PP/PE/PP PP/PE/PP PP/PE/PP PP/PE/PP PP/PE/PP PE/PP/PEPE/PP/PE PE/PP/PE PE/PP/PE PE/PE/PE Des- PP 60% PP 65% PP 65% PP 65% PP65% PP 65% PP 58% PP 42% PP 42% PP 42% PP 0% PP cription Thickness, 26.9  15.7   9.5  13.0  15.7   18.6   19.9   9.4   9.8  16.5  17.2 17.1 μm Thickness   0.72   0.46   0.37   0.46   0.45    0.65    0.55  0.49   0.45   0.51   0.60   0.54 std dev JIS Gurley,  540  485  391 427  550   560 —  283  195  373  517  364 second Shrinkage   2.7   0.8  0.7   0.9   1.6    1.6    1.5   2.8   5.4   1.7   3.7   7.2 @ 90° C.for 1 hour, % Elongation   52/   73/  88/  90/   79/    73/    99/   87/  63/  68/   77/  75/ at break in  478  928  36  93  416   963   116 964  869 1031  967 1022 MD/TD, % Modulus in 5170/ 5425/ 5166/ 4724/5764/  5959/  2969/ 2957/ 3645/ 2833/ 3846/ 2979/ MD/TD, 2421 3413 58805507 4431  4021  2348 1866 2409 1766 1973 2266 kg/cm² Tensile 1925 21332115 1749 2075  2006  1830 2077 1891 1923 1740 1925 strength in MD,kg/cm² Tensile  146  193  187  181  154   170   163  199  188  176  157 120 strength in TD, kg/cm² Puncture  502 373 for  177  252  365   421  357  183  154  255  243  283 Strength, g PP side/ 218 for PE side ER,ohm-   1.92   2.05   1.31   1.87   1.70    2.00    2.30   1.11   0.89  1.42   1.81   1.63 cm² Mixed  130  110  89  112  105   123   122  70 67  104  118  103 Pene- tration, kgf Dielectric 2900 2082  823 15632337 2,341 2,568  754 1040 1476 1769 1564 Break- down, volts Porosity, 40.3  38  30  38  34   41   40  36  43  43  37  44 %

TABLE 2 Examples of Polymer Blends with Ceramic TiO₂ to Improve MeltingIntegrity Comparison #1 Sample #1 Sample #2 Sample #3 Sample #4Description PE/PE/PE PE/PP/PE PP/PE/PP PP/PE/PP PE/PE/PE trilayertrilayer PE trilayer PE trilayer PE trilayer 65% in 35% 58% thickness inthickness in thickness Additive no additives 30% TiO2 in 20% TiO2 in 20%TiO2 in 20% TiO2 in the middle the middle the middle the middle layerlayer layer layer Thickness, μm/thickness 17.1/0.54 17.8/0.40 15.3/0.6115.9/0.44 15.5/0.46 std dev JIS Gurley, sec 364 500 400 267 193Shrinkage @ 90° C. for 1 7.2 5.3 2.2 1.6 4.6 hour, % Tensile strength inTD, 120 110 148 180 100 kg/cm² Puncture strength, g 283 310 288 257 265ER, ohm-cm² 1.63 1.76 2.60 1.53 1.08 Mix Penetration, kgf 103 102 99 10487 Dielectric Breakdown, volts 1564 1586 1973 1643 1179 Porosity, % 43.543.5 41.5 45.0 46.6 Aquapore Size, μm 0.055 0.030/0.057 — 0.035/0.0910.064 Peel Strength or Adhesion, >60 >60 >60 >60 >60 g High TemperatureMelt 0% 13% 15% 20% 10% Integrity @250° C. by TMA

TABLE 3 Examples of Polymer Blends Comparison Sample Sample SampleSample Sample Sample Sample Sample Sample Number #1 #1 #2 #3 #4 #5 #6 #7#8 Description PP/PE/PP PP/PE/PP PP/PE/PP PP/PE/PP PE/PE/PE PE/PE/PEPP/PE/PP PP/PE/PP PP/PE/PP trilayer trilayer with trilayer with trilayertrilayer with trilayer with trilayer trilayer trilayer without 5% 5000ppm with 2% 15% PE wax 30% PE with 10% with 20% with 10% additivesethoxylated Kemamide ® antistatic in the middle wax in the talc in talcin talc in alcohols in in the outside additive layer to middle outsideoutside outside the middle layers to Pelestat lower the layer to PPlayer PP layer PP layer layer to improve pin 300 in the shutdown lowershut and 20% and 25% and 25% improve removal outside temperature downTiO2 in TiO2 in TiO2 in wettability performance layer temperature thethe the middle middle middle PE layer PE layer PE layer to to to improveimprove improve melt melt melt integrity integrity integrity Thickness,(μm) 16.0 15.5 15.5 17.3 20.6 20.3 18.3 18.0 17.5 Gurley, sec 35 35 3537 13 13-25 56 60 44 Wettable No Yes — — — — — — — Shutdown 130 130 130130 127 124 130 130 130 Temp,° C. High 0% 0% 0% 0% 0% 0% >20% >20% >20%Temperature Melt Integrity @ 250° C. Pin Removal, g 9100 — 8400 — — — —— —

The present invention may be embodied in other forms without departingfrom the spirit and the essential attributes thereof, and, accordingly,reference should be made to the appended claims, rather than to theforegoing specification, as indicated the scope of the invention.

1. A battery separator comprising: a co-extruded, microporous membranehaving at least two layers made of extrudable polymers and having auniform thickness defined by a standard deviation of <0.80 μm, whereinthe co-extruded, microporous membrane has a thickness from 8 to 25microns.
 2. (canceled)
 3. (canceled)
 4. The battery separator of claim 1wherein an extrudable polymer of one of said at least two layers is thesame or different than an extrudable polymer of another of said at leasttwo layers.
 5. The battery separator according to claim 1 wherein atleast one of said extrudable polymers is a thermoplastic polymer.
 6. Thebattery separator according to claim 1 wherein at least one of saidextrudable polymers is selected from the group consisting of:polyolefins, polyamides, polyvinylidenes, copolymers of the foregoing,and blends thereof.
 7. The battery separator according to claim 1wherein at least one of said extrudable polymers further comprises amaterial added thereto.
 8. The battery separator according to claim 7wherein said material is selected from the group of materials adapted todo at least one of the following: lower the melting temperature of theextrudable polymers; improve the melt integrity of the membrane; improvethe strength of toughness of the membrane; improve the antistaticproperties of the membrane; improve the surface wettability of theseparator; improve the surface tribology performance of the separator;improve the processing of the extrudable polymers; improve the flame ofthe membrane; facilitate nucleation of the extrudable polymers; colorthe layer of the membrane; and combinations thereof.
 9. A batteryseparator comprising: a co-extruded, microporous membrane having atleast two layers made of extrudable polymers and having an interplyadhesion as defined by a peel strength >60 grams.
 10. The batteryseparator according to claim 9 wherein at least one of said extrudablepolymers is a thermoplastic polymer.
 11. The battery separator of claim9 wherein an extrudable polymer of one of said at least two layers isthe same or different than an extrudable polymer of another of said atleast two layers.
 12. The battery separator according to claim 9 whereinat least one of said extrudable polymers is selected from the groupconsisting of: polyolefins, polyacetals, polyamides, polyesters,polysulfides, polyvinyl alcohols, polyvinyl esters, polyvinylidenes,copolymers of the foregoing, and blends thereof.
 13. The batteryseparator according to claim 9 wherein at least one of said extrudablepolymers further comprises a material added thereto.
 14. The batteryseparator according to claim 13 wherein said material is selected fromthe group of materials adapted to do at least one of the following:lower the melting temperature of the extrudable polymers; improve themelt integrity of the membrane; improve the strength of toughness of themembrane; improve the antistatic properties of the membrane; improve thesurface wettability of the separator; improve the surface tribologyperformance of the separator; improve the processing of the extrudablepolymers; improve the flame retardancy of the membrane; facilitatenucleation of the extrudable polymers; color the layer of the membrane;and combinations thereof. 15.-18. (canceled)
 19. The battery separatoraccording to claim 1 wherein said membrane is a dry-stretched membrane.20. The battery separator according to claim 9 wherein said membrane isa dry-stretched membrane.
 21. A lithium ion battery comprising thebattery separator of claim
 1. 22. A lithium ion battery comprising thebattery separator of claim
 9. 23. (canceled)
 24. The battery separatorof claim 4 wherein the extrudable polymer of one of said at least twolayers is different than an extrudable polymer of another of said atleast two layers, and wherein dissimilar polymer refers to: polymershaving dissimilar chemical natures (e.g., PE and PP, or PE and aco-polymer of PE are polymers having dissimilar chemical natures),and/or polymer having the same chemical nature (e.g., PP1 and PP2, or PPand a co-polymer of PP are polymers having similar chemical natures) butdissimilar properties (e.g., two PE's or PP's having differingproperties (e.g., density, molecular weights, molecular weightdistributions, rheology, additives (composition and/or percentage),etc.).
 25. The battery separator of claim 4 wherein an extrudablepolymer of one of said at least two layers is polymerically dissimilarfrom an extrudable polymer of another of said at least two layers. 26.The battery separator of claim 4, wherein the extrudable polymer of theone of said at least two layers comprises a first polypropylene, andwherein the extrudable polymer of the another of said at least twolayers comprises a second polypropylene, said second polypropylenehaving a density, molecular weight, molecular weight distribution,rheology, additives (composition and/or percentage), and/or the likedifferent from said first polypropylene.
 27. The battery separator ofclaim 11 wherein the extrudable polymer of one of said at least twolayers is different than an extrudable polymer of another of said atleast two layers, and wherein dissimilar polymer refers to: polymershaving dissimilar chemical natures (e.g., PE and PP, or PE and aco-polymer of PE are polymers having dissimilar chemical natures),and/or polymer having the same chemical nature (e.g., PP1 and PP2, or PPand a co-polymer of PP are polymers having similar chemical natures) butdissimilar properties (e.g., two PE's or PP's having differingproperties (e.g., density, molecular weights, molecular weightdistributions, rheology, additives (composition and/or percentage),etc.).
 28. The battery separator of claim 11 wherein an extrudablepolymer of one of said at least two layers is polymerically dissimilarfrom an extrudable polymer of another of said at least two layers. 29.The battery separator of claim 11, wherein the extrudable polymer of theone of said at least two layers comprises a first polypropylene, andwherein the extrudable polymer of the another of said at least twolayers comprises a second polypropylene, said second polypropylenehaving a density, molecular weight, molecular weight distribution,rheology, additives (composition and/or percentage), and/or the likedifferent from said first polypropylene.
 30. The battery separatoraccording to claim 4 wherein said membrane is a dry-stretched membrane.31. The battery separator according to claim 11 wherein said membrane isa dry-stretched membrane.
 32. A lithium ion battery comprising thebattery separator of claim
 4. 33. A lithium ion battery comprising thebattery separator of claim
 11. 34. A membrane comprising: a co-extruded,microporous membrane having at least two layers made of extrudablepolymers and having a uniform thickness defined by a standard deviationof <0.80 μm, wherein the co-extruded, microporous membrane has athickness from 8 to 25 microns.
 35. The membrane of claim 34 wherein anextrudable polymer of one of said at least two layers is the same ordifferent than an extrudable polymer of another of said at least twolayers.
 36. The membrane according to claim 34 wherein at least one ofsaid extrudable polymers is a thermoplastic polymer.
 37. The membraneaccording to claim 34 wherein at least one of said extrudable polymersis selected from the group consisting of: polyolefins, polyvinylidenes,copolymers of the foregoing, and blends thereof.
 38. The membraneaccording to claim 34 wherein at least one of said extrudable polymersfurther comprises a material added thereto.
 39. The membrane accordingto claim 38 wherein said material is selected from the group ofmaterials adapted to do at least one of the following: lower the meltingtemperature of the extrudable polymers; improve the melt integrity ofthe membrane; improve the strength of toughness of the membrane; improvethe antistatic properties of the membrane; improve the surfacewettability of the separator; improve the surface tribology performanceof the separator; improve the processing of the extrudable polymers;improve the flame of the membrane; facilitate nucleation of theextrudable polymers; color the layer of the membrane; and combinationsthereof.
 40. A membrane comprising: a co-extruded, microporous membranehaving at least two layers made of extrudable polymers and having aninterply adhesion as defined by a peel strength >60 grams.
 41. Themembrane according to claim 40 wherein at least one of said extrudablepolymers is a thermoplastic polymer.
 42. The membrane of claim 40wherein an extrudable polymer of one of said at least two layers is thesame or different than an extrudable polymer of another of said at leasttwo layers.
 43. The membrane according to claim 40 wherein at least oneof said extrudable polymers is selected from the group consisting of:polyolefins, polyacetals, polyamides, polyesters, polysulfides,polyvinyl alcohols, polyvinyl esters, polyvinylidenes, copolymers of theforegoing, and blends thereof.
 44. The membrane according to claim 40wherein at least one of said extrudable polymers further comprises amaterial added thereto.
 45. The membrane according to claim 44 whereinsaid material is selected from the group of materials adapted to do atleast one of the following: lower the melting temperature of theextrudable polymers; improve the melt integrity of the membrane; improvethe strength of toughness of the membrane; improve the antistaticproperties of the membrane; improve the surface wettability of theseparator; improve the surface tribology performance of the separator;improve the processing of the extrudable polymers; improve the flameretardancy of the membrane; facilitate nucleation of the extrudablepolymers; color the layer of the membrane; and combinations thereof. 46.The membrane according to claim 34 wherein said membrane is adry-stretched membrane.
 47. The membrane according to claim 40 whereinsaid membrane is a dry-stretched membrane.
 48. A lithium ion batterycomprising the membrane of claim
 34. 49. A lithium ion batterycomprising the membrane of claim
 40. 50. The membrane of claim 35wherein the extrudable polymer of one of said at least two layers isdifferent than an extrudable polymer of another of said at least twolayers, and wherein dissimilar polymer refers to: polymers havingdissimilar chemical natures (e.g., PE and PP, or PE and a co-polymer ofPE are polymers having dissimilar chemical natures), and/or polymerhaving the same chemical nature (e.g., PP1 and PP2, or PP and aco-polymer of PP are polymers having similar chemical natures) butdissimilar properties (e.g., two PE's or PP's having differingproperties (e.g., density, molecular weights, molecular weightdistributions, rheology, additives (composition and/or percentage),etc.).
 51. The membrane of claim 35 wherein an extrudable polymer of oneof said at least two layers is polymerically dissimilar from anextrudable polymer of another of said at least two layers.
 52. Themembrane of claim 35, wherein the extrudable polymer of the one of saidat least two layers comprises a first polypropylene, and wherein theextrudable polymer of the another of said at least two layers comprisesa second polypropylene, said second polypropylene having a density,molecular weight, molecular weight distribution, rheology, additives(composition and/or percentage), and/or the like different from saidfirst polypropylene.
 53. The membrane of claim 42 wherein the extrudablepolymer of one of said at least two layers is different than anextrudable polymer of another of said at least two layers, and whereindissimilar polymer refers to: polymers having dissimilar chemicalnatures (e.g., PE and PP, or PE and a co-polymer of PE are polymershaving dissimilar chemical natures), and/or polymer having the samechemical nature (e.g., PP1 and PP2, or PP and a co-polymer of PP arepolymers having similar chemical natures) but dissimilar properties(e.g., two PE's or PP's having differing properties (e.g., density,molecular weights, molecular weight distributions, rheology, additives(composition and/or percentage), etc.).
 54. The membrane of claim 42wherein an extrudable polymer of one of said at least two layers ispolymerically dissimilar from an extrudable polymer of another of saidat least two layers.
 55. The membrane of claim 42, wherein theextrudable polymer of the one of said at least two layers comprises afirst polypropylene, and wherein the extrudable polymer of the anotherof said at least two layers comprises a second polypropylene, saidsecond polypropylene having a density, molecular weight, molecularweight distribution, rheology, additives (composition and/orpercentage), and/or the like different from said first polypropylene.56. The membrane according to claim 35 wherein said membrane is adry-stretched membrane.
 57. The membrane according to claim 42 whereinsaid membrane is a dry-stretched membrane.
 58. A lithium ion batterycomprising the membrane of claim
 35. 59. A lithium ion batterycomprising the membrane of claim 42.